Method of energy transfer to a heterogeneous fluid medium utilizing a fluid convection plasma jet

ABSTRACT

A process for energizing a fluid medium containing an entrained condensed phase by means of an arc discharge between an anode and a cathode having a conical tip, said arc discharge forming a contraction of the current-carrying area in the transition region in the vicinity of said cathode, the points of inflection of said contraction of the current-carrying area forming, when extended, an angle Alpha , which comprises forcefully projecting a fluid medium along said conical tip of said cathode into and through said contraction of the current-carrying area in the transition region in the vicinity of said cathode at a mass flow density at substantially constant convection rate which is at least sufficient to effect a rise in the temperature of said arc column at a constant current level and below a total fluid medium convection rate at substantially constant mass flow density which is sufficient to reduce the angle Alpha below 40* at a constant current level, and adding a finely dispersed nongaseous medium capable of causing an enlargement in the angle Alpha , to said fluid medium forcefully projected along said conical tip at a total fluid medium convection rate at substantially constant total mass flow density which is below that sufficient to reduce said enlarged angle Alpha below 40* at a constant current level.

OZ-22-72 XR United States Patent Sheer et al.

[ Feb. 22, I972 [54] METHOD OF ENERGY TRANSFER TO A HETEROGENEOUS FLUID MEDIUM UTILIZING A FLUID CONVECTION 21 Appl.No.: 1,390

Related US. Application Data [63] Continuation-impart of Ser. No. 805,574, Mar. 10,

The Fluid Transpiration Arc as a Radiation Source For Solar Simulation Semiannual Progress Report" by C. Sheer and S. Korman, P- 3/312, AFOSR67- 2363, Jan. 1, 1967 to June 30; 1967.

Product and Technical Information" By Tafa Division (Humphrey' s Corp.), lnre Transpiration Cooled Plasma Torch," Jan., 1969.

Primary Examiner-Roy Lake Assistant Examiner-Palmer C. Demeo Attorney-Hammond & Littell [57] ABSTRACT A process for energizing a fluid medium containing an entrained condensed phase by means of an arc discharge between an anode and a cathode having a conical tip, said are discharge forming a contraction of the current-carrying area in the transition region in the vicinity of said cathode, the

points of inflection of said contraction of the current-carrying area forming, when extended, an angle a, which comprises forcefully projecting a fluid medium along said conical tip of said cathode into and through said contraction of the currentcarrying area in the transition region in the vicinity of said cathode at a mass flow density at substantially constant convection rate which is at least sufficient to effect a rise in the temperature of said are column at a constant current level and below a total fluid medium convection rate at substantially constant mass flow density which is sufficient to reduce the angle abelow 40 at a constant current level, and adding a finely dispersed nongaseous medium capable of causing an enlargement in the angle a, to said fluid medium forcefully projected along said conical tip at a total fluid medium convection rate at substantially constant total mass flow density which is below that sufficient to reduce said enlarged angle or below 40 at a constant current level.

6 Claims, 5 Drawing Figures PATENTEDFEB 22 I972 SHEET 1 OF 3 INVENTORS CHARLES SHEER smut L K can AN ATTORNEYS PATENTEDFEBZZ I97? 3 44 7 1 SHEET 2 [IF 3 |.2- EFFECT OF INJECTION VELOCITY on EFFLUENT PLASMA TEMPERATURE a; aacouncs'ra) 0.8- r gas 0.6- 1 NITROGEN (rcsn) "o 0.4-

c I l l l l l 2 4 o s B l0 l2 m(GRAMS Cm c.

wmoow ancuzocvs convccnou RATE ARGON GAS o y 0 FCC WITH 30 com-1 ANGLE L E G EN D -5OAMP- ARC.CURRENT u-IOOAMP. ARC.CURRENT 5 IO IS 5:0 M COVECTION RATE (GM wars???" F 4 smuzLxoamm SHEET 3 OF 3 INVENTORS CHARLES SHEER SAMUEL KORMAN METHOD OF ENERGY TRANSFER TO A I-IETEROGENEOUS FLUID MEDIUM UTILIZING A FLUID CONVECTION PLASMA JET REFERENCE TO EARLIER FILED APPLICATIONS copending 10, 1969 THE PRIOR ART As is well known, a hierarc is an electric discharge between a cathode and an anode of such intensity that the material of the anode face is vaporized and converted into a plasma jet, shooting off into space, avoiding the cathode. This is sometimes referred to as the consumable anode hierarc.

Methods and devices for transferring energy to fluid materials also by exposing said fluid material to the energy of a hierarc have been previously reported. For example, in U.S. Pat. No. 3,209,193, a novel method of exposing the fluid to the energy of an arc is disclosed, which consists of passing the fluid continuously through a porous anode so that it enters the discharge via the active anode surface, i.e., where said surface is acting as the arc terminus. That patent further discloses that unique and valuable results can be obtained if certain criteria are satisfied in operating such a device.

Specifically, the performance criteria required to achieve the desired results are the following:

I. The average diameter of the pores on the surface of the anode is less than the thickness of the anode fall space which is normally established in the absence of fluid flow adjacent to the active area, i.e., the fall space thickness of a conventional are operating under no-flow conditions.

2. The fluid is forced to flow through the passageways in the porous electrode so that the fluid emerges directly from the electrode surface into the fall space over the area integrally congruent with the arc terminus on the porous electrode surface, and preferably nowhere else.

3. The surface distribution of orifices, through which the fluid emerges from the electrode into the fall space, is sufficiently uniform that the individual streams of fluid from each orifice will diffuse laterally, merging with each other stream adjacent to it to form a homogenous stream, as through it were issuing as a vapor from a solid surface, and further, the average interorifice distance on the active surface is sufficiently small that essentially complete flow homogeneity is established before the fluid penetrates an appreciable distance into the fall space.

4. For a given are current, gap distance, and ambient pressure, the rate of fluid transpiration through the porous anode is adjusted so that it is greater than the value required to effect a transition to the hierarc mode of arc operation.

U.S. Pat. No. 3,214,623 describes an improvement to the above patent where the arc discharge has an essentially conical geometry. The cathode, porous anode and insulating supports are arranged geometrically to each other, so that the conduction column assumes the shape of an axially symmetrical conical shell.

The technique of fluid injection through a porous anode has been termed the fluid transpiration arc" (FTA), and is a second example of the use of a hierarc to transfer energy to materials.

Several interesting features distinguish the FTA from the other forms of plasma generators and which emphasize the potential utility of this technique as an addition to the roster of high temperature devices. One of the most striking properties of the FTA is the energy transfer efficiency (ratio of effluent.

jet enthalpy to power input). This results largely from the elimination of the need for thermal constriction of the arc column, which is the basic means of stabilizing the column against fluid flow in the wall-stabilized arc. in the latter device, a large fraction (e.g., 30 to 60 percent) of the power input is unavoidably lost by heat transfer to the cooling circuit of the constricting channel. In the case of the FTA, when the fluid emerging from the porous anode penetrates the anode sheath, an overabundance of ions are created which serve to stabilize the arc, irrespective of flow rate. Hence the need for a watercooled constricting channel, which is a major energy sink, is eliminated. An additional factor is the regeneration of heat transferred to the body of the anode, some of which is transferred to the incoming gas as it transpires through the anode and returned to the arc stream. This reduces the power lost to the cooling circuit of the anode holding structure, thus further improving the efficiency. The net result is a plasma generator which, even for the small laboratory units, operates with efflciencies in the range of to percent.

Another consequence of the elimination of the column constriction is the quasi free-burning nature of the FTA. The only constraint involved in this device is the requirement that the working fluid penetrate the anode sheath as it emerges from the anode. Since the sheath is a thin layer contiguous to the anode surface, the column formed by the stream after it leaves the sheath is completely unencumbered. This is of interest for applications in which virtually complete accessibility of the effluent column provides an important practical advantage. Also of interest is the quasi one-dimensional character of the emergent plasma for an appreciable distance along the column. Owing to the shape and disposition of the anode sheath (thin, flat disc) through which the fluid passes, the plasma properties of the emerging column are relatively invariant in the radial direction. Furthermore, the radial invariance persists for several column diameters downstream, providing an appreciable volume characterized by only axial variation of plasma parameters. This means that a small axial increment of the column may be treated as a uniform medium, thus vastly simplifying the theoretical interpretation of diagnostic data.

One of the most interesting features of the FTA is the abnormally high electrical conductivity of the effluent plasma, particularly in the region near the anode. Here one observes a macroscopic plasma zone characterized by a high degree of nonequilibrium. In particular, the electron temperature is much higher than the gas temperature throughout most of this region. This feature has been observed in low pressure 0.1 atm.) discharges, but never before at atmospheric pressure. The high electron temperature is in itself insufficient to explain the measured electrical conductivity (two-temperature model). Spectroscopic measurements indicate a higher degree of ionization than can be correlated with the Saha equation. The high density of free electrons in a relatively dense plasma suggests an enhancement of continuum radiation and provides the basis for an efficient source of radiation.

Attempts have also been made to inject a working fluid into the interior of an arc column at other points than the anode. Many difficulties have been found in these attempts. For example, in a constricted arc column having a conventional wallstabilized arc with a segmented, water-cooled constrictor channel long enough to assure the establishment of a fully developed column, the injected gas was forced to flow axially, concentric and parallel to the conduction column. Since the column in this device is subject to an appreciable thermal constriction, it would seem that the convected gas would be forced through the column boundary into the primary energydissipating zone. lt was found, however, that, even in the fully developed region, beyond which the radial distributions of the flow parameters remain constant, by far the major part of the flow traverses the thin, cool, nonconducting gas film adjacent to the channel wall. In fact only about l0 percent of the mass flow enters the hot core. The much higher density and lower viscosity of the cool gas in the wall layer, plus the fact that even a very thin film can have appreciable cross-sectional area near the wall, compensate for the lower velocity of the cool gas layer, and account for nearly all of the convected mass flow. lt should.be noted that the radial temperature across the fully developed portion of the column remains above 10,000

K. over 80 percent of the channel diameter, so that the plasma fills the channel quite well. The conclusion is that most of the working fluid does not penetrate the column and is therefore not directly exposed to the zone of maximum energy dissipation.

The same effect is noted with other flow configurations. For example, if a stream of gas is projected at right angles to the column ofa free-burning arc, the arc will be blown out at quite low flow rates. However, the column can be stabilized by a magnetic field of suitable strength oriented normal to both column and gas flow so as to balance exactly the force of convection. Even when the balance is established at very high flow rates, the gas does not enter the column, but is deflected around it, the column behaving much like a solid cylinder. An examination of existing arc jet devices reveals that in nearly every case most of the working fluid is not subjected to the zone of direct energy transfer. The only exception previously known is the FTA in which the working fluid is first energized in the anode sheath and then fully permeates the column in the vicinity of the anode. Even in this device, however, when used with a conventional conically tipped cathode, the natural cathode jet collides with the transpiration gas at some point between the electrodes. Hence, the injected gas permeates only the positive column," i.e., the portion of the conduction column between the anode and the point of impingement of the two jets. The negative column" (between the cathode tip and the point of impingement) is characterized by the flow of ambient gas which may not be the same as the injected gas.

OBJECTS OF THE INVENTION An object of the present invention is the development of a method of adding increased amounts of a nongaseous working fluid into the negative column extending form the cathode tip.

Another object of the present invention is the development of a process of energizing a fluid medium containing an entrained condensed phase by means of an arc discharge between an anode and a cathode having a conical tip, said discharge forming a contraction of the current-carrying area in the transition region in the vicinity of said cathode, the points of inflection of said contraction of the current-carrying area forming, when extended, an angle a, which comprises forcefully projecting a fluid medium along said conical tip of said cathode into and through said contraction of the currentcarrying area in the transition region in the vicinity of said cathode at a mass flow density at substantially constant convection rate which is at least sufficient to effect a rise in the temperature of said are column at a constant current level and below a total fluid medium convection rate at substantially constant mass flow density which is sufficient to reduce the angle or below 40 at a constant current level, and adding a finely dispersed non-gaseous medium capable of causing an enlargement in the angle a, to said fluid medium forcefully projected along said conical tip at a total fluid medium convection rate at substantially constant total mass flow density which is below that sufficient to reduce said enlarged angle a below 40 at a constant current level.

These and other objects of the invention will become more apparent as the description thereof proceeds.

THE DRAWINGS FIG. 1 is a schematic diagram illustrating the arc column contraction and the angles a in the vicinity of the cathode.

FIG. 2 is an enlarged cross section of operation of the method of the invention including the cathode.

FIG. 3 is a graph of the temperature rise during the process of the invention.

FIG. 4 is a graph of the reduction in the angle a with increased convection rate at constant current level and mass flow densities.

FIG. 5 is a medial section of one embodiment of the operation of the process of the invention. s

DESCRIPTION OF THE INVENTION It has long been known that when an arc is struck between an anode and a cathode having a conical tip, as illustrated in FIG. 1, there occurs a contraction of the current-carrying area in the transition region between the cathode l and the column proper 2. This contraction is indicated as the contraction zone 3. This contraction of the current-carrying area in the transition region between the cathode l and the column proper 2 i may also be defined by the angle a which is determined by extending lines tangent to the column boundary at the points of inflection 25 of the contraction. This contraction causes the natural cathode jet effect as explained in the following.

Referring to FIG. 1, the current density, and therefore, the self-magnetic field due to the arc current, increases toward the cathode as a result of the contraction. This nonuniform magnetic field exerts a body force on the conductive plasma, propelling it in the direction of maximum decrease in magnetic field, i.e., along the arc axis away from the cathode tip. The streaming of plasma away from the cathode tip decreases the local pressure in the immediate vicinity of the cathode tip and causes the arc to aspirate gas from the surrounding atmosphere. This mechanism establishes the well-known cathode jet, which has been observed to flow along the axis of the column away from the cathode tip in all arcs characterized by a contraction zone adjacent to the cathode.

In our concurrently filed US. Pat. application Ser. No. 1,388 we show that this contraction zone 3 can serve as an injection window across which a fluid medium in the form ofa gas may be injected directly into the arc column 2 at flow rates in excess of what can be forced across the cylindrical column boundary of the arc. Gas flow rates of a magnitude much greater than that aspirated naturally can be injected into the column without disturbing the stability of the arc when the gas is forced to follow the conical configuration of the cathode tip. However, the increase in gas convection rate does effect the angle a and if the angle a is reduced below 40, no substantial amounts of addition gas can be injected into the arc column 2. The effect of the forced convection is to increase the voltage gradient in and near the transition region, thereby increasing the volume rate of energy dissipation and making available the additional energy needed to heat the increased quantity of gas introduced to the column temperature. In

short, the injection of a copious stream of gas into the column through the injection window is not only possible but actually increases the heat transfer effectiveness of this part of the are, as long as it does not exceed the convection rate which will reduce the angle at below 40.

The boundaries of the gas which is forced to follow the conical configuration of the cathode tip are on the one hand the surface of the cathode, and on the other hand a line parallel to the surface of the cathode which intersects the cathode column at the outermost limit of the contraction zone 3. Preferably, the gas is forced to follow the conical configuration of the cathode tip in such a manner that its essential entirety enters the contraction zone at its region of maximum convergence. This region can be determined by trial.

In the aforesaid application a cone" with reference to the cathode is defined as a converging segment which may be a true cone having a circular cross section or may be pyramidal in shape, comprising a number of converging planar surfaces whose cross section is a polygon of any convenient number of sides. The term cone angle refers to the vertex angle of the converging segment.

Although many are systems have been used in which the working fluid is convected to the are via an annular passage concentric to the cathode, the effect described in the aforesaid application has not previously been noted due to the special conditions of gas injection which is required to produce the maximum effect. For this purpose, the gas to be injected must be projected in a high velocity layer along the conical cathode surface.

By proper adjustment of the gas velocity and cone angle of the cathode. the gas can be made to cross the column boundary in essentially the same general direction as would the aspirated ambient gas stream in the absence of forced convection. The optimum cone angle for this purpose appears to be between 45 and 60. 7

The cone angle is disclosed as an important parameter. Variations in cone angles from and 135 may be employed depending partially on the material of the cathode, the type of fluid material injected, and the work purpose of the device. A

cone angle in the range of to 60 is preferably and, more particularly, 45 to 60 are utilizable with good results.

A second critical parameter is the injection velocity. This can be varied without'altering the total mass flow (convection) rate by varying the area of the annular orifice and changing the inlet gas pressure as required to maintain a fixed flow rate. It has been observed, for example, that as the injection velocity (mass flow density) is varied the column temperature passes through a peak, with the maximum temperature rising to two r0 three times that obtained when the velocity is several times higher or lower than its optimum value. It should also be mentioned that the creation of a high velocity gas layer flowing along the surface of the cathode is effective in regenerating some of the heat lost by thermal conduction back from the cathode tip.

A third critical parameter is the total mass flow of the injected fluid medium. As the total mass flow of the injected fluid medium is varied at substantially constant current level and mass flow density, an alteration of the shape of the contraction zone 3 occurs. When the total mass flow or convection rate of the injected fluid medium is increases from zero, little or no change in the shape of the contraction zone 3 is observed and substantially all of the injected fluid enters the arc column through the injection window. However, as the total mass flow of the injected fluid medium is increased further, at a point depending on the medium injected, the contraction zone begins to elongate thus decreasing the space rate of contraction of the arc column diameter. This space rate of contraction may be called the window angle and is depicted in FIG. I as the angle a. When the angle a is sufficiently reduced, that is, to about 40 or less, the major portionofthe flow of the fluid medium does not enter the arc column.

The above technique of injecting the working fluid into the contraction region of the column is termed the forced convection cathode" arc (FCC). Excellent operational stability is achieved without energy-wasting thermal constraints, providing the basis for excellent efficiency along with a high degree of accessibility to the primary energy transfer zone. Together with the FTA it provides a means whereby the working fluid can be made to penetrate significantly all portions of the conduction column, from anode to cathode, absorb otherwise unavailable energy in the electrode transition zones, and regenerate some of the heat normally lost to the electrodes.

By the use of the FCC many chemical and physical reactions may be conducted in a practical manner. For example, a gas such as nitrogen, argon orhydrogen can be introduced into the injection window and in a highly energized condition is projected so as to contact an anode. The emerging plasma jet may be utilized to heat other materials, for example, in cutting and welding.

In addition a reactive gas, such as nitrogen or hydrogen, can be introduced as above into the injection window to form a highly energized plasma jet which is projected into the jet of plasma vapor issuing from the anode of a consumable anode hierarc. If such an anode is a carbon anode, and hydrogen is introduced through the FCC, the mixture of the two jets is favorable to the production of hydrocarbons. Further, where the consumable anode contains a metal or metaloid, then if hydrogen or nitrogen is injected through the FCC, the gases to projected will unite with the plasma of the hierarc to form the corresponding nitride or hydride of the metal of the anode.

In addition, by the use of a combination of the FCC and the FTA, two different gases may be introduced into the cathode injection window and the anode fall space, respectively, to perform such operations as the synthesis and reformation of -organic compounds and inorganic compounds such as amdroplets or solid particles, and that said liquid or solid particu-.

lates will be carried through the injection window along with the carrier gas to mingle with the column and be exposed to the high temperature environment therein more effectively and at greater material throughput rates than any prior art device operating at equivalent power levels. A number of highly useful applications are derived from this capability. For example, using an inert gas such as argon, virtually any powdered material, including metals, oxides, etc., may be passed through the are at such a rate relative to the power level that the material is melted, but not appreciably vaporized, during its transit through the column and effluent jet. When allowed to condense, following emergence from the jet, such materials will congeal in a spherical form, which is useful in powder metallurgy and other applications. By allowing the molten droplets to impinge on a substrate, the familiar process of flame spraying may be achieved with greater material application rates and better quality coatings than otherwise possible.

Also by reducing the rate of material throughput relative to the power level, the entrained particulates can be made to vaporize during their passage through the arc zone. Upon emerging from the jet, the vapors will recondense into extremely fine particles in the submicron range, thus providing an efficient process for the comminution of coarser powdered materials.

It has now been found that when the FCC is brought to operate in a steady state in the above manner, an increase in the convection rate of the heterogeneous material, while the gaseous material being introduced is held at a constant convection rate, causes an enlargement of the window angle a. As shown in FIG. 1, after a steady state equilibrium is reached at any convection rate at a constant current level and at an optimum mass flow density, the window angle is angle a. Introduction into the fluid medium injected of a finely divided nongaseous material causes an enlargement of the window angle, shown as angle a This effect is due to an enlargement of the arc column which is observed to occur whenever the injected gas stream contains significant amounts of liquid or solid material entrained in the gas as small droplets or particles. It is believed to be caused by the vapor pressure generated by vaporizing particles in the column core which would be expected to cause a radial expansionof the column. This view is consistent with the observations that except very near the cathode, the column enlarges radially with the introduction of a heterogeneous feed along its entire length, and that the enlargement increases with distance away from the cathode, i.e., the column shape changes from that ofa cylinder to a more or less diverging cone as shown in the dotted lines of FIG. 1. Of particular interest is the fact that the area of the cathode spot does not change with heterogeneous feed. Hence the space rate of column diameter decreases in the contraction zone and, therefore, the window angle, increases with heterogeneous feed as is illustrated by the dotted lines and angle (1 in FIG. 1.

This enlargement of the window angle occurs, as indicated, after the introduction into the gaseous injected feed of finely divided liquids or solids which vaporize in the column core and are, therefore, capable of enlarging the window angle. Since the temperature in the column core' is in excess of 10,000 K., most particulated solids will undergo some degree of vaporization. The enlargement of the angle a will depend on the material introduced and, therefore, varies somewhat. This enlargement of the window angle is unexpected since if a heterogeneous feed material such as a gaseous carrier material and a finely divided nongaseous material dispersed therein are originally introduced through the FCC, an optimum operational state is reached within the area where the velocity of the feed at constant flow rate and current level is sufficient to effect a rise in the temperature of the arc column and below a total fluid medium convection rate at constant mass flow density and current level sufficient to reduce the angle at below 40. Thereafter, introduction ofa further amount of the finely dispersed nongaseous medium in the heterogenous feed thus increasing the total convection rate, act also to enlarge the window angle 11, thus enabling an increase in the partial convection rate of the nongaseous material up to the point where the enlarged angle a is reduced below 40. It has been found that it is difficult to attain a stable arc column if a heterogeneous feed is originally introduced at a total convection rate equal to that obtained by the above procedure.

FIG. 2 is a cross section of a cathode nozzle 4 designed to optimize a gas injection into the arc column 2 via the injection window at the contraction zone 3 at the end of the cathode 1. For this purpose, the nozzle 4 forms a narrow annular orifice 6, upstream of the conical cathode tip 7, directing the gas 5 to flow in a high-velocity layer along the conical cathode surface.

The injection velocity of the injected fluid medium can be varied by varying the area of the narrow annular orifice 6. This is based on the following well known formula:

pv =M/A where p= a density of the fluid medium at the orifice v velocity of the fluid medium at the orifice A total mass flow of fluid medium through the orifice A area of the orifice By adjusting the axial position of the nozzle, it is clear that the orifice area, A, will change. It is a simple matter to maintain the mass flow, M, constant by adjusting the inlet pressure and observing the flow rate with a flowmeter. This, therefore, provides variation in the quantity, pv, which is in effect the momentum per unit volume of the gas stream emerging from the orifice and is equal to the mass flow density referred to as the nozzle orifice. This is actually the fundamental parameter governing the effect being illustrated. However, we have found that under most conditions under which this device is operated, including those of these experiments, the changes in head pressure required to maintain M constant were very slight so that there is very little change in the density, p, during the experiment. The mass flow density is, therefore, a very good indication of gas velocity at the nozzle orifice, and because of its close proximity, the velocity with which the gas enters the injection window. However, since the measured quantities are M and A, we shall define riz=MlA and present the results of each test as a plot ofrii versus the intensity of a monochromator output which gives an indication of temperature. The results are presented in FIG. 3. Both curves clearly show a peak verifying the existence of an optimum injection velocity. The specific performance data for these tests are as follows:

In order to determine the window angle a, the total mass flow or convection rate M is varied at constant arc current and mass flow density. The configuration of the arc column 2 in the contraction zone 3 was visually inspected as the total mass flow M is varied.

, ally defined in FIG. 1 and is designated a."

In summary, we have found that as M increases or decreases and that as a decreases, the effectiveness of the window in admitting the convected fluid into the column is reduced. When a is sufficiently reduced, to about 40 or less, the major portion of the flow does not enter the column and the value of the device as a heat transfer device becomes severely limited.

An example of the effect of M on a a utilizing a cathode with a 30 cone angle and argon as the injected fluid medium is depicted in FIG. 4. In this FIG. two curves are drawn, for 50 a. and a., respectively, showing the variation of a with M. These results indicate that the maximum total argon gas throughput rate that can be energized by injection into the arc column in the manner described, when a cathode with a 30 cone angle is used operating at 50 a. are current, is about 30 g. of argon per minute. This is obtained from the 50 a. curve of FIG. 8 where oz=40 as a minimum. The value for rii was 67 g./sec./cm 100 a. of arc current the same value ofa shows the maximum M is increased to about 0 grams per minute The value for rh was 4.5 g./sec./cm

This effect is relatively independent of Iii, which is the mass flow density referred to the annular nozzle orifice 6. This is given by the ratio M/A where A is the orifice area and is approximately proportional to the injected gas velocity. The following table illustrates the effect of rh on a for a fixed are current of a. and a fixed total mass flow M of 12 grams per minute utilizing argon.

ril (g./sec./cm.) a (degrees) Within experimental error the value of a can be taken as having remained unchanged for a nearly tenfold increase in m. Thus when M is held below the maximum value for efficient injection, it is possible to adjust in to its optimum value for maximum energy transfer to the gas without changing a, i.e., without disturbing the degree of penetration of the feed into the arc column.

In order to take advantage of the effect of the enlargement ofthe window angle a on introduction of a nongaseous material capable of enlarging the window angle a and the arc column, preferably the arc is started with only gas (homogenous) feed. Then when conditions are optimized (nozzle orifice adjusted for maximum column temperature, with M well below the value required to keep a above 40) the solid or liquid material is entrained in the gas (heterogenous feed) starting off with a low amount of solids (e.g., l or 2 grams per minute) and increasing the fraction until the mass flow of solids is comparable to that of the carrier gas (e.g., 10 to 30 g./min.). At this point the enlargement in the window angle will permit the total mass flow (entrained solids plus carrier gas) to be increased still further without serious loss of penetration into the column. The amount of effective increase in the material feed to the arc column will depend on a variety of factors, including the arc current, the ratio of carrier gas to entrained material and the nature of both carrier gas and the solid or liquid particles. With relatively nonrefractory solid materials and with most liquid materials, a twofold or greater partial convection rate (nongaseous material) can be obtained. With more refractory solid materials, an improvement in the partial convection rate (nongaseous material) of 25 to 5 0 percent can be attained.

For each combination of carrier gas and condensed phase component, the upper limit of M for a given are current must be determined experimentally. When this is properly done and when the proper starting procedure is used, the capability of the device in heating heterogenous feeds to'plasma temperature is significantly enhanced.

In other chemical applications a reactive gas such as hydrogen may be used as the carrier gas to entrain powdered coal so as to produce a mixture of active hydrogen and carbon vapor, from which acetylene and other hydrocarbons may be condensed. Alternatively, droplets of liquid hydrocarbons may be entrained in the hydrogen for hydrocarbon reformation. Similarly, metals or metalloidal powders may be entrained in hydrogen or nitrogen to produce hydrides or nitrides. The introduction of metal oxides with hydrogen to produce metals, or with ammonia to produce nitrides, may also be accomplished. Many other similar applications for chemical processing are possible in which greater efficiency and higher yields are obtainable from the use of this process than can be obtained from other methods of treatment. When a particulated solid is introduced through the annular orifice, we have found that no difficulties in flow occur as long as the size of the particles is less than the width of the annular orifice,

preferably onethird to one-fourth the orifice.

The principle by which this cathode gas stream is employed is illustrated in FIG. 2 in which is shown a conical cathode 1 over which the cathode gas 5 is caused to flow over the conical surface of the cathode l and beyond the tip 7. With such a construction, some of the heat energy from the body of the cathode 1 has been found to be transmitted to the gas stream 5 when the gas stream is mechanically caused to hug the conical cathode l by means of the annular nozzle 6. The construction shown in FIG. 5 shows the apparatus for conducting the process wherein the cathode fluid medium is energized to form a plasma jet which contacts a water-cooled solid anode. The cathode l and cathode nozzle 4 are depicted as in FIG. 2. The are column 2 emitting from the cathode tip 7 is directed to and contacts a water-cooled solid anode 9, such as a watercooled copper block. The plasma jet 8 flows away from the anode.

The following example illustrates the practice of the invention. It is not to be construed, however, as limitative in any respect.

width of the annular EXAMPLE The device utilized is shown diagrammatically without the anode in FIG. 2 and with the anode in FIG. 5. It consists ofa tungsten rod three-eighth inch in diameter having a conical tip with a 60 cone angle as the cathode. Surrounding the cathode is an enveloping nozzle 4 having a conical section whose inside surface also has a cone angle of 60 so that it mates with the conical cathode surface. The conical section of the nozzle is truncated so that it terminates several millimeters behind the cathode tip 7, and thus forms an annular orifice 6 about the cathode. The annular passage between the nozzle and cathode is effective in directing the flow of input fluid material 5 in the form of converging conical layer flowing close to the cathode surface, finally impinging on the arc column 2 largely on the injection window of the contraction zone 3.

For a given orifice area, the mass flow rate of gas can be controlled by adjusting the inlet pressure, and, for the experiment being described was varied from as little as 2 grams per minute of argon gas to over 50 grams per minute.

The nozzle itself was initially fabricated of boron nitride ceramic, although, owing to its proximity to the arc, in later tests it was found expedient to make the nozzle out of a metal such as brass and provide it with a separate water cooling circuit to prevent overheating. However, in the latter case, care was taken to insulate the nozzle electrically from the cathode to avoid the formation of undesired secondary arcs.

The orifice area of the cathode nozzle is made variable by moving the nozzle section relative to the cathode in the axial direction. This is done by mounting the nozzle itself on a micrometer screw. Rotation of the nozzle in either direction thus causes the latter to move horizontally relative to the sta tionary cathode, opening or closing the nozzle orifice. In the present example various nozzle orifice areas were used varying from 1.00 to 4.5 square millimeters, corresponding to the annulus widths ofO. l 8 mm. to 1.16 mm.

The anode 9 of the arc in this apparatus is composed of a one inch diameter copper tube with /a-inch thick wall, closed at one end with a rounded cap which serves as the currentreceiving area. The interior of the tube is fitted with water passages and the anode is vigorously water cooled to inhibit erosion of the surface during operation. Provision is made to change the position of the anode with respect to the cathode, thus effectively varying the arc gap. It was also found convenient for starting the arc to provide means for altering the angle as well as the position of the anode rod with respect to the cathode axis. The procedure used for igniting the arc is as follows.

The anode is rotated about 45 and raised so that the rounded end of the anode points toward the cathode tip, and the cathode axis intersects the anode rod near its center. Simultaneously, the anode rod is brought close to the cathode tip, to leave a gap of about 5 mm. After adjusting the cathode nozzle orifice area to a suitable value, usually about 3 square millimeters, a moderate flow of gas is turned on. For argon, a startup flow of 10 to 15 grams per minute was usually used. The arc is then ignited, using a momentary high frequency spark to form a conductive path between the electrodes with the main power supply turned on, following which a rapid spark to are transition occurs. This technique of arc ignition is well known in the art.

Once the art is ignited, generally with a starting current of about 50 amps, the arc gap is increased to its desired value by withdrawing the anode. The anode is rotated to a convenient lateral position, preferably normal to the arc axis, and retracted so that the end cap is just below the plasma stream. In this configuration the effluent jet leaves the conduction column in essentially the axial direction. For high flow rates care must be taken to keep the end of the anode sufficiently close to the column to prevent the are from being blown out.

The following are the pertinent operating parameters for the start up operation to attain stable operation of the arc.

Arc current: 50 to 300 amperes Arc voltage: 35 to 165 volts Arc gap: 1 to 12 centimeters Total mass flow or argon: 2 to 50 grams per minute Cathode nozzle orifice area: 1.00 to 4.5 square millimeters When conditions are optimized (nozzle orifice adjusted for maximum column temperature, with M well below the value required to keep a about 40) the solid or liquid material is entrained in the argon (heterogeneous feed) starting off with a low amount of solids (e.g., l or 2 grams per minute) and increasing the fraction until the mass flow of solids is comparable to that of the argon (e.g., 10 to 30 g./min.). At this point the enlargement in the window angle will permit the total mass flow (entrained solids plus carrier gas) to be increased still further without serious loss of penetration into the column. The amount of effective increase in material feed to the arc column will depend on a variety of factors, including the arc current, the ratio of carrier gas to entrained material, and the nature of both carrier gas and the solid or liquid particles. Using a relatively nonrefractory solid such as B 0 in argon gas at a. are current, a twofold increase in carrier gas injection rate could be sustained before significant amounts of feed material could be observed to be deflected from the column.

With a more refractory material such as SiO under the same conditions, the improvement was in the range of 30 to 40 percent. For each combination of carrier gas and condensed phase component, the upper limit ofM for a given are current must be determined experimentally. When this is properly done and when the proper starting procedure is used, the capability of the device in heating heterogeneous feeds to plasma temperature is significantly enhanced.

The preceding specific embodiment is illustrative of the practice of the invention. It is to be understood, however, that other expedients known to those skilled in the art may be performed without departing from the spirit of the invention.

We claim: I

l. A process of energizing a fluid medium containing an entrained condensed phase by means of an arc discharge between an anode and a cathode having a conical tip, said are discharge forming a contraction of the current-carrying area in the transition region in the vicinity of said cathode, the points of inflection of said contraction of the current-carrying area forming, when extended, an angle a, which comprises establishing an arc discharge between said anode and said cathode, forcefully projecting a fluid medium along said conical tip of said cathode into and through said contraction of the current-carrying area in the transition region in the vicinity of said cathode at a mass flow density at substantially constant convection rate which is at least sufficient to effect a rise in the temperature of said are column at a constant current level and below a total fluid medium convection rate at substantially constant mass flow density which is sufficient to reduce the angle at below 40 at a constant current level, and adding a finely dispersed nongaseous medium capable of causing an enlargement in the angle a, to said fluid medium forcefully projected along said conical tip at a total fluid medium convection rate at substantially constant total mass flow density which is below that sufiicient to reduce said enlarged angle at below 40 at a constant current level.

2. The process of claim 1 wherein said fluid medium is a gas.

3. The process of claim 1 wherein said fluid medium is a reactive gas.

4. The process of claim 1 wherein said finely dispersed nongaseous medium is a liquid.

5. The process of claim 1 wherein said finely dispersed nongaseous medium is a nonrefractory solid.

6. The process of claim 1 wherein said finely dispersed nongaseous medium is a refractory solid. 

1. A process of energizing a fluid medium containing an entrained condensed phase by means of an arc discharge between an anode and a cathode having a conical tip, said arc discharge forming a contraction of the current-carrying area in the transition region in the vicinity of said cathode, the points of inflection of said contraction of the current-carrying area forming, when extended, an angle Alpha , which comprises establishing an arc discharge between said anode and said cathode, forcefully projecting a fluid medium along said conical tip of said cathode into and through said contraction of the current-carrying area in the transition region in the vicinity of said cathode at a mass flow density at substantially constant convection rate which is at least sufficient to effect a rise in the temperature of said arc column at a constant current level and below a total fluid medium convection rate at substantially constant mass flow density which is sufficient to reduce the angle Alpha below 40* at a constant current level, and adding a finely dispersed nongaseous medium capable of causing an enlargement in the angle Alpha , to said fluid medium forcefully projected along said conical tip at a total fluid medium convection rate at substantially constant total mass flow density which is below that sufficient to reduce said enlarged angle Alpha below 40* at a constant current level.
 2. The process of claim 1 wherein said fluid medium is a gas.
 3. The process of claim 1 wherein said fluid medium is a reactive gas.
 4. The process of claim 1 wherein said finely dispersed nongaseous medium is a liquid.
 5. The process of claim 1 wherein said finely dispersed nongaseous medium is a nonrefractory solid.
 6. The process of claim 1 wherein said finely dispersed nongaseous medium is a refractory solid. 